package class06;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class FindFirstIntersectNode3 {

    public static class Node {
        public int value;
        public Node next;

        public Node(int data){
            value = data;
        }
    }

    public static Node getLoopNode(Node head){
        if (head==null||head.next==null||head.next.next==null)
            return null;
        Node slow = head.next;
        Node fast = head.next.next;
        while (slow!=fast){
            if (fast.next==null||fast.next.next==null)
                return null;
            slow = slow.next;
            fast = fast.next.next;
        }
        fast = head;
        while (fast !=slow){
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }

    public static Node noLoop(Node head1,Node head2){
        if (head1==null&&head2==null)
            return null;
        Node cur1 = head1;
        Node cur2 = head2;
        int n = 0;
        while (cur1.next!=null){
            n++;
            cur1 = cur1.next;
        }
        while (cur2.next!=null){
            n--;
            cur2=cur2.next;
        }
        if (cur1!=cur2)
            return null;
        cur1 = n>0?head1:head2;
        cur2 =cur1==head1?head2:head1;

        while (n!=0){
            n--;
            cur1 = cur1.next;
        }
        while (cur1!=cur2){
            cur1=cur1.next;
            cur2 = cur2.next;
        }
        return cur1;
    }

    public static Node bothLoop(Node head1,Node loop1,Node head2,Node loop2){
        Node cur1 = null;
        Node cur2 = null;
        if (loop1==loop2){
            cur1 = head1;
            cur2 = head2;
            int n = 0;
            while (cur1!=loop1){
                n++;
                cur1 = cur1.next;
            }
            while (cur2!=loop2){
                n--;
                cur2 = cur2.next;
            }
            cur1=n>0?head1:head2;
            cur2=cur1==head1?head2:head1;
            n = Math.abs(n);
            while (n!=0){
                n--;
                cur1 = cur1.next;
            }
            while (cur1!=cur2){
                cur1 =cur1.next;
                cur2=cur2.next;
            }
            return cur1;
        }else {
            cur1 = loop1.next;
            while (cur1!=loop1){
                if (cur1 == loop2)
                    return loop1;
                cur1 = cur1.next;
            }
            return null;
        }
    }

    public static Node getIntersectNode(Node head1,Node head2){
        if (head1 == null||head2==null)
            return null;
        Node loop1 = getLoopNode(head1);
        Node loop2 = getLoopNode(head2);
        if (loop1==null&&loop2==null)
            return noLoop(head1,head2);
        if (loop1!=null&&loop2!=null)
            return bothLoop(head1,loop1,head2,loop2);
        return null;
    }
}
